# Thread: Poisson distribution, university exam quistion

1. ## Poisson distribution, university exam quistion

I have the following exam question witch I would appreciate some help with

Question:
In certain parts of a car one uses plastic plates. These plates can have cracks. The number of cracks in a plate has a Poisons distribution with mean
Labda =0.02

a) One inspects 50 plates. What is the probability that the number of plates with two or more cracks is larger than two?

There are 50 plates therefore i would say 50 * labda = 1

Probability of 2 cracks with 50 plates =
P(x=0) + P(x=1) + P(x=2)
for more then 2 it is 1- (P(x=0) + P(x=1) + P(x=2))

Formula = P(X=k) = e^-labda * (labda^k / k!)

=1-0.368-0.368-0.18=0.0842

How to solve the part with "more than 2 cracks"
Ore how are these related.

2. ## Re: Poisson distribution, university exam quistion

hi,
just think a bit about what P(x=k) means and how you include the knowledge that you are dealing with 50 plates into the formula. That would help with the first questions.

Regarding the last one you have a probability of 1 for the event "less the 2 cracks" OR "exactly 2 cracks" OR " more then 2 cracks". if you can calculate the first two terms you can express the third.

regards
rogojel

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